The present invention relates to a wireless tire condition monitoring apparatus that permits a driver in a vehicle passenger compartment to check the conditions of tires, such as the air pressure.
Wireless tire condition monitoring apparatuses that allow a driver in a vehicle passenger compartment to check the conditions of vehicle tires have been used. One such monitoring apparatus includes transmitters. Each transmitter detects condition, such as the pressure and the temperature, of an associated tire, and wirelessly transmits data representing the detected tire conditions. A receiver for receiving the data from the transmitters is provided on the vehicle body.
The transmitters are each provided in a tire attached to the vehicle. The receiver includes reception antennas each corresponding to one of the transmitters. Each reception antenna induces a voltage that corresponds to the electric field strength of radio waves transmitted from the corresponding transmitter. To obtain necessary data from voltage signals induced by the reception antennas, the receiver processes the voltage signals.
When receiving data, the receiver must distinguish which one of the transmitters has wirelessly sent the data. Accordingly, to distinguish one of the antennas that has the greatest level of induced voltage, in a prior art device disclosed in Japanese Laid-Open Patent Publication No. 10-104103, the receiver uses a multiplexer circuit to switch the reception antennas such that only one of the antennas is activated at a time. The antenna that is activated when the voltage signal level is highest is determined to be the closest one to the transmitter that has sent data. Thus, the positions of the tires are determined.
However, in the configuration of the prior art device, the number of the reception antennas must be equal to the number of the tires. Also, to increase the level of induced voltage, each reception antenna must be located in the vicinity of the corresponding tire, which limits the method for installing the antennas.
In addition, while awaiting signals from the transmitters, the multiplexer circuit must be kept activated to receive voltage signals from all the reception antennas. This increases power consumption.
Further, since only one of the reception antennas is activated at a time to distinguish the transmitters, the level of each obtained voltage signal is relatively low. Therefore, it is difficult to perform the distinction procedure of the transmitters accurately and reliably.